Hydrocracking process for benzcoronene-contaminated feedstocks

ABSTRACT

Mineral oil feedstocks which contain dissolved benzcoronenes are subjected to hydrocracking over certain catalysts based on a steam treated, metal-cation-deficient Y zeolite while maintaining a sufficient recycle of unconverted oil to bring about, in systems using non-steam-treated Y zeolite catalysts, a substantial buildup and eventual precipitation of benzcoronenes in cooler parts of the systems such as heat exchange surfaces. According to the invention, this buildup and precipitation is prevented by virtue of the higher activity of the steam-treated Y zeolite catalysts for conversion of benzcoronenes, as compared to the more conventional non-steam-treated Y zeolite catalysts.

United States Patent Ward Feb. 19, 1974 [5 HYDROCRACKING PROCESS FOR3,715,303 2 1973 Wennerberg et al. 208/112 BENZCORONENE CONTAMINATED3,725,244 4/1973 Schutt 208/59 3,726,787 4 1973 Frazier et a1 2011 59FEEDSTOCKS John W. Ward, Yorba Linda, Calif.

Union Oil Company of California, Los Angeles, Calif.

Filed: Jan. 30, 1973 Appl. No.2 328,102

Related US. Application Data Continuation-impart of Ser. No. 241,434,April 5, 1972, abandoned.

Inventor:

Assignee:

US. Cl 208/111, 208/48 R, 208/59,

252/455 Z Int. Cl..... C10g 9/16, ClOg 13/02, C01b 33/28 Field of Search208/111, 59, 48

References Cited UNITED STATES PATENTS Primary Examiner-Delbert E. GantzAssistant Examiner-G. E. Schmitkons Attorney, Agent, or Firm-Milton W.Lee

[57] ABSTRACT Mineral oil feedstocks which contain dissolvedbenzcoronenes are subjected to hydrocracking over certain catalystsbased on a steam treated, metal-cationdeficient Y zeolite whilemaintaining a sufficient recycle of unconverted oil to bring about, insystems using non-steam-treated Y zeolite catalysts, a substantialbuildup and eventual precipitation of benzcoronenes in cooler parts ofthe systems such as heat exchange surfaces. According to the invention,this buildup and precipitation is prevented by virtue of the higheractivity of the steam-treated Y zeolite catalysts for conversion ofbenzcoronenes, as compared to the more conventional non-steam-treated Yzeolite catalysts.

18 Claims, N0 Drawings I-IYDROCRACKING PROCESS FORBENZCORONENE-CONTAMINATED FEEDSTOCKS RELATED APPLICATION I Thisapplication is a continuation-in-part of copending application Ser. No.241,434 filed Apr. 5, 1972 and now abandoned.

BACKGROUND AND SUMMARY OF INVENTION The catalytic hydrocracking ofmineral oil feedstocks using Group VIII metal promoted Y zeolitecatalysts has in recent years become an established commercial process.This process offers substantial advantages over older hydrocrackingprocesses in respect to catalyst life, liquid yields, reduced dry gasmake, and lower operating temperatures and pressures. A difficulty wasencountered however in respect to the use of such catalysts forhydrocracking feedstocks containing dissolved benzcoronenes, and where asubstantially total recycle of unconverted oil was maintained. Thesebenzcoronene contaminants are not known to be native constituents ofcrude oils, or any of the virgin distillates therefrom. Neither havethey been detected in the unconverted oils from conventional catalyticcracking, coking, thermal cracking, or the like. They are soluble inhydrocarbon oils only to the extent of a few parts per million, up toperhaps about 100 parts per million for the more soluble species. Theavailable evidence indicates that these benzcoronenes find their wayinto refinery streams via synthesis in high temperature hydroconversionssuch as reforming, or catalytic hydrofining at temperatures above about700F. As is well known,

- posed, the tendency of these benzcoronenes to cause coking anddeactivation of the catalyst; the relatively low temperatures and highhydrogen pressures employed tend to prevent further polymerizationand/or condensation reactions of such compounds to form coke. Instead,the principal problem which has evolved is peculiar to those processeswherein substantially all of the heavy unconverted product fraction iscontinuously recycled in the process. Conventional Y zeolite catalystsapparently do not hydrogenate benzcoronenes at a rate sufficient toprevent their buildup in the recycle system. Due to their low solubilityin the oil, when the concentration of such compounds builds'up to alevel of about 50-100 parts per million, they begin to plate out? incooler portions of the system, particularly heat exchange surfaces,transfer lines, valves and the like, resulting in plugging problems andreduced heat exchange efficiency. conventionally, this problem is solvedby bleeding a portion of the recycle oil from the system, but this isundesirable from several standpoints, including reduced yields of morevaluable products such as gasoline.

Another solution to this problem is the subject of U. S. Pat. No.3,505,208, and involves the addition of ammonia to the hydrocrackingzone. For reasons which are not clearly understood, the ammonia appearsto bring about an increased rate of conversion of the benzcoronenes toother compounds which are more soluble in the liquid product. However,the use of ammonia presents an additional operational complication, andthe liquid product ordinarily requires water washing to remove theammonia. It would be more desirable from several standpoints to providea catalyst which itself possessed the inherent activity required forconverting the benzcoronenes.

It has now been discovered that this desired intrinsic activity isexhibited by a class of recently developed Y zeolite catalysts in whichthe zeolite component has been subjected to a high temperature steamtreatment while in an ammonium form, a hydrogen form, or a decationizedform, or mixtures thereof. The objective of these steam treatments,several of which are disclosed in the prior art, was not to improve thecatalytic activity for benzcoronene conversion, but to render thecatalysts more resistant to hydrothermal degradation, i.e., loss ofsurface area and crystallinity upon contact with water or water vapor.For reasons which are not clearly understood, it appears that the steamcalcination treatments bring about some physical and/or chemical changein the zeolite base which renders it not only more resistant tohydrothermal degradation, but also renders the combination thereof witha Group VIII metal hydrogenating component more active for thehydrodecomposition of benzcoronenes.

DESCRIPTION OF FEEDSTOC KS Broadly speaking, any mineral oil feedstockmay be employed herein which contains benzcoronenes in amountssufficient to result in a buildup thereof to levels above theirsolubility limits in a recycle hydrocracking process utilizingconventional Y zeolite catalysts. In some cases, amounts as low as oneweight part per million may be sufficient to result in such undesirablebuildup, although in general amounts greater than about 5 parts permillion are required. It is noteworthy that coronene itself, eitherbecause of greater solubility and/or greater ease of conversion byconventional Y zeolite catalysts, does not appear to be troublesome. Thetroublesome benzcoronenes are defined herein as any fused-ringpolycyclic aromatic hydrocarbon containing a coronene nucleus and fusedthereto at least one additional benzo-ring. Examples of such compoundswhich have been found in solid deposits removed from heat exchangers areas follows:

Benzcoroncnes (-44 Z) Naphbenzcoronenes Dibenlcoronenes Dibenzcoronenesf 0 Q) W E; )U I l l Ovalenes Tribenzcoronenes TribenzcoronenesBenzovalenes HY: U l

Tetrabenzcoronenes only in mineral oils of similarly highend-boiling-points (as determined by conventional ASTM methods). Sincethe limit of solubility of these compounds ranges between about 10 andparts per million, their presence in mineral oils has little or noeffect upon endboiling-points thereof as determined by conventionalmethods. Hence, it may be found that feedstocks with end-boiling-pointsas low as about 500F may contain troublesome amounts of benzcoronenes.

As noted above, benzcoronenes are generally found PROCESS DESCRIPTION Inbroad aspect, the invention simply involves passing the desiredfeedstock along with added hydrogen through a hydrocracking unitcontaining a steamcalcined Y zeolite catalyst as hereinafter described,cooling and condensing the resulting product, fractionating it torecover the desired low boiling product, e. g., gasoline and/or jetfuel, and finally recycling sufficient unconverted oil to bring about,under normal conditions utilizing a conventional Y zeolite catalyst, abuildup of benzcoronenes to levels exceeding their solubility in theliquid product condensate. Thus, the invention is not limited to a totalrecycle of unconverted oil, although one of the most advantageousaspects of the invention is that it does permit total recycle. Operativehydrocracking conditions are as follows:

HYDROCRACKING CONDITIONS Broad Range Preferred Range Temperature, F.450-850 500-750 Pressure, psig 5004,000 600-3,000 LHSV 0.4-20 l-lOH,/Oil Ratio, MSCF/B 3-l5 4-10 450 650F. are normally preferred. Wheregasoline is the major desired product, it is normally preferred tooperate at relatively high temperatures in the range of about 650 850F.,in the presence of at least about 50 ppm of hydrogen sulfide in order toobtain a more aromatic high-octane product.

DESCRIPTION OF CATALYSTS Effective catalysts for use herein comprise ingeneral deficient Y zeolite, the resulting ammonium zeolite is calcinedunder substantially dry conditions at temperatures of about 600 1,800F.,preferably about 800 1,650F., to decompose the zeolitic ammonium ionsand produce the desired hydrogen and/or decationized zeolite. Whenintimately composited with a hydrogenating metal such as palladium, thismaterial forms ahighly active hydrocracking catalyst, but is nothydrothermally stable and does not display the desired intrinsicactivity for converting benzcoronenes.

To achieve the desired activity for converting benzcoronenes, as well ashydrothermal stability, the calcination step referred to above iscarried out at temperatures of about 950 1,800F., preferably about l,lO1,650F., and in the presence of at least about 0.2 psi of water vapor,preferably about to psi. It is not essential that steam be presentduring the entire calcination; it is entirely feasible to carry out adry calcination to effect deammoniation and formation of a conventionalmetal-cation-deficient zeolite, and thereafter carry out the steamcalcination to give the desired hydrothermal stability and activity forbenzcoronene conversion. Any suitable procedure may be utilized formaintaining the necessary water vapor partial pressure in contact withthe zeolite during at least an effective portion of the calcinationtreatment. In one modification, the wet zeolite from the exchange stepcan merely be heated in a covered container so as to retain the watervapor generated therefrom. Alternatively the zeolite can be introducedinto a batch or continuous rotary furnace, or a static bed calcinationzone, into which preheated steam or humidified air is introduced. Theduration of steam treatment is at least about 0.5 minutes, preferablyabout 30 minutes to about 4 hours. Suitable steam treatments aredescribed more in detail in U. S. Pat. No. 3,354,077.

One effect oflthe steam calcination is a reduction in the unit cell sizeof the zeolite. This parameter can be used as a measure of the requiredsteaming severity for the present purposes. The factors, time,temperature and water vapor partial pressure should be correlated so asto effect at least about 0.2 percent, and preferably at least about 0.4percent, reduction in unit cell size, from the cell size of the originalsodium Y zeolite.

If desired, the steam stabilized zeolite produced as above described canbe subjected to a second ammonium ion exchange step to further reducethe sodium content thereof, and the resulting product then againcalcined, preferably under dry conditions, to effect deammoniationthereof. The second calcination is conducted at temperatures betweenabout 750 and ble, but is stable in the presence of ammonia and watervapor.

A herein preferred modification of the stabilized zeolite describedabove is prepared by carrying out the final calcination after mixing thezeolite with a finely divided, hydrous metal oxide such as alumina, asdescribed more particularly in my co-pending application Ser. No.191,123, filed Oct. 11, 1971. The resulting composition is alsohydrothermally stable and stable in the presence of ammonia and watervapor. This preferred zeolite is prepared as follows:

The initial sodium Y zeolite starting material, containing about 10-14weight-percent of sodium as N a O, is first digested in conventionalmanner with an aqueous solution of a suitable ammonium salt such as thechloride, nitrate, sulfate, carbonate, acetate, etc., to replace atleast about 20 percent but not more than about 95 percent, of theoriginal sodium ions with ammonium ions. The sodium content should bereduced to about 0.6 5 percent, preferably about 1-4 percent by weight,as Na O. To reduce the sodium level to this value, it may be desirableto employ two or more stages of exchange treatments. If it is desired toremove less than about 50 percent of the sodium in this step, diluteacids, e.g., 0.01N I-INO may be used instead of ammonium salts. Theinitialsteam calcination is then carried out as described above.

The resultant steam-calcined zeolite is then reexchanged with ammoniumsalt solution under sufficiently severe conditions to reduce the sodiumcontent to less than about 3 weight-percent, usually less than onepercent, and preferably less than about 0.6 weightpercent, as Na O. Itshould be realized that this second exchange treatment does notintroduce any appreciable amount of ammonium ions into the exchangesites which were converted to hydrogen ion and/or decationized sites inthe first calcination step; nearly all of the ammonium ions which gointo the zeolite at this point do so by replacing remaining sodium ions.Since a substantial ammonium zeolite moiety is desired in the finalcalcination step for conversion to active exchange sites during thefinal calcination, it will be apparent that sufficient sodium should beinitially present at the second exchange step to permit a substantialportion of the ion exchange capacity to become satisfied by ammoniumions. Accordingly, the zeolite subjected to the second ion exchange stepshould contain sufficient sodium remaining from the first exchange stepto provide in the double-exchanged zeolite an amount of ammonium ioncorresponding to at least about 5 relative percent, preferably 10-20percent, of the original ion exchange capacity of the zeolite.

Prior to the final calcination step, preferably following the secondexchange step, the zeolite component is intimately admixed with a finelydivided, hydrous, refractory oxide of a difficultly reducible metal. Theterm hydrous is used to designate oxides having structural surfacehydroxyl groups detectable in infra red analysis. The preferred oxidesare alumina, silica, magnesia, beryllia, zirconia, titania, thoria,chromia, and combinations thereof such as silica-alumina,silica-magnesia, and the like. Naturally occurring clays comprisingsilica and alumina may also be utilized, preferably after acidtreatment. The resulting mixtures may contain between about 0.5 and 98weight-percent of zeolite, preferably at least about 2 weight-percent,and generally about 5 to about weight-percent, based on the combined dryweight of the zeolite and the metal oxide. The metal oxide can becombined with the zeolite as a hydrous sol or gel, as an anhydrousactivated gel, a spray dried powder or a calcined powder. In onemodification a sol or solution of the metal oxide precursor such as analkali metal silicate or aluminate can be precipitated to form a gel inthe presence of the zeolite.

When less hydrous forms of the metal oxide are combined with thezeolite, essentially any method of effecting intimate admixture of thecomponents may be utilized. One such method is mechanical admixture,e.g., mulling, which involves admixing the zeolite in the form of apowder with the slightly hydrous, finely divided form of the metaloxide. Minor amounts of water, with or without an acidic peptizing agentsuch as a strong mineral acid, are usually added to facilitateadmixture.

After admixing the hydrous oxide with the zeolite component, it isnormally preferable at this point to form the mixture into the shapedesired for the final catalyst. Conventional tableting, prilling, orextruding procedures may be utilized to produce tablets, prills orextrudate pellets having a diameter of about one thirtysecond inch tothree-eighths inch. Other conventional pelleting aids may be added suchas lubricants, binders, diluents, etc.

The pelleted zeolite-metal oxide composition is then subjected to asecond calcining at temperatures between about 750 and 1,300F.,preferably about 800 1,000F. lt is preferred to maintain a relativelyanhydrous environment during this second calcination. If there is asubstantial water vapor partial pressure during this step, the finalcatalyst is usually less active than those produced in the substantialabsence of water vapor. Accordingly, this calcination is preferablyconducted in the presence of less than 2, and preferably less than about1, psi of water vapor. The calcination may be regarded as complete whensubstantially all water and ammonia have been expelled from thecatalyst, which, depending on the temperature employed,

may range between about 10 minutes and 12 hours or more. a

The necessary metal hydrogenation component may be distributedselectively on the'zeolite component of the catalyst, or on the metaloxide component. Alternatively it may be distributed more or lessequally on both components. Effective hydrogenation components comprisethe Group VIB and/or Group VIII metals and their oxides and/or sulfides,with or without other metals such as rhenium. Operative proportions(based on free metal) may range between about 0.1 percent and 30 percentby weight, depending upon the type of metal or metals selected, and thedesired activity. In the case of the Group VIII noble metals, amounts inthe range of 0.1 to about 2 percent will normally be employed; the irongroup metals, iron, cobalt and nickel, are normally utilized inproportions of about 1-10 weight-percent; the Group VIB metals willnormally be utilized in proportions of about 3-20 weight-percent.Preferred hydrogenating metals are palladium, platinum, nickel, cobalt,tungsten and molybdenum. Particularly preferred are palladium, orcombinations of nickel and/or cobalt with molybdenum and/or tungsten.

The hydrogenating component may be added to the catalyst at any desiredstage in its manufacture. Preferred methods include impregnation and/orionexchange of soluble metal salts into the powdered zeolite after thesecond ammonium ion exchange, or into the catalyst pellets prior to thefinal calcination step. Other methods include mixing of soluble orinsoluble compounds of the desired metal or metals with the powderedzeolite-hydrous metal oxide mixture prior to extruding or pelleting.

The following examples are cited to demonstrate the superiorbenzcoronene conversion activity of the catalysts of this invention, butare not to be construed as limiting in scope:

EXAMPLE I A palladium-zeolite-alumina catalyst (A) of this invention wasprepared as follows: Sodium Y zeolite having a SiO /AI O mole-ratio ofabout 4.8 was repeatedly ion exchanged with excess ammonium sulfatesolution until the sodium content thereof was reduced to 1.7weight-percent of Na O. The zeolite was then recovered by filtration andactivated by steaming at 700C for one hour in contact with about 15 psiof water vapor. The steaming reduced the unit cell size of the zeoliteby about 0.7 percent. Reexchange with ammonium sulfate further reducedthe sodium content to 0.2' weight-percent Na O. This material was thensubjected to ion exchange with an aqueous ammoniacal solution ofpalladium tetramminochloride, Pd( NH Cl, in proportions sufficient tointroduce 0.65 weight-percent palladium metal into the zeolite(corresponding to 0.5 weight-percent palladium in the finalcomposition).

An extrudable paste was then prepared by mixing sufficient proportionsof the zeolite, alumina and water to provide a finished productcontaining weightpercent zeolite and 20 weight-percent alumina on a dryweight basis. The paste was then extruded and calcined in air bygradually increasing the temperature of the extrudate to 930F. over afive hour period, and holding at that temperature for an additional onehour. Throughout the final calcining, dry'aircontaining less than 0.5psi water vapor was passed over the zeolite supported on a porous gridin the'calcination furnace.

EXAMPLE II I The catalyst of Example I was tested for hydrocrackingactivity in comparison with a more conventional Y zeolite catalyst (B)containing 0.5% Pd. The zeolite base for this catalyst was prepared byexchanging the original sodium Y zeolite with an ammonium salt solutionto reduce the sodium content to about 1 percent Na O, followed byback-exchange with magnesium sulfate solution to introduce stabilizingzeolitic magnesium ions equivalent to about 3 weight-percent MgO. Theproduct was then slurried with water and about 20 weight-percent (drybasis) of alumina gel, and the palladium was added as described inExample I. The wet filter cake was then dried, pelleted and dry-calcinedsubstantially as described for the second calcination in Example I.

Catalysts A and B were then tested for hydrocracking activity in anintegral hydrofining-hydrocracking system inwhich the raw feed was firsthydrofined in conventional manner to reduce the organic nitrogen contentto about 1 ppm, and the entire hydrofiner effluent was then passedthrough the respective hydrocracking catalyst bed A or B, withtemperature controlled to gasoline, and in the second zone to give about60 percent conversion per pass. In each run, pressures, space velocitiesand hydrogen ratios were essentially the same in the respectivecontacting zones. The significant results were as follows:

Table 3 Days on stream Benzcoronene content, ppm

Effluent from first hydrocracking zone Feed to second hydrocracking zone(includes recycle oil from second zone Table 1 Catalyst Time on stream,Hrs. 247 169 Coronene and Benzcoronene content, ppm

In hydrofiner effluent 1.7 1.8 In hydrocracker recycle oil 3.5 9.0

Upon repeating these runs at 775 psig and 1.0 space It is apparent thatcatalyst A is much more active than catalyst B for convertingbenzcoronenes. The results with catalyst B would be even less favorableif ammonia from the hydrofiner had not been present in the hydrocrackingzone. I

(The raw feed employed in this example boiled between 400 and 850F., hada gravity of 23.8 API, and contained 1.3 weight-percent sulfur and 0.22weightpercent nitrogen.)

EXAMPLE III This example demonstrates that the catalysts of thisinvention do not require the presence of ammonia for effectivebenzcoronene conversion, while catalyst B of Example II compares evenless favorably in the absence of ammonia.

In this example, the feed of Example II was integrally hydrofined andhydrocracked as described in Example II, but instead of recyclingunconverted oil from the hydrocracking zone back to that zone, it wassubjected to separate recycle hydrocracking in an ammonia-freehydrocracking zone containing the same catalyst as the firsthydrocracking zone. In one run, both hydrocracking zones containedcatalyst A, while in the other, both contained a catalyst substantiallyidentical to catalyst B. Temperatures in the first zone were controlledto give about 40 volume percent conversion per pass to Catalyst It isthus apparent that catalyst A performed much better in bothhydrocracking zones than did catalyst B; but the difference is much moredramatic in the ammonia-free second zone to which unconverted oil wasbeing recycled.

It is not intended that the invention should be limited to the detailsdescribed above. The following claims and obvious equivalents thereofare intended to define the true scope of the invention.

I claim:

1. A process for hydrocracking a mineral oil feedstock which has beenpreviously hydrofined at temperatures above about 700F. which comprisescontacting said feedstock plus added hydrogen and under hydrocrackingconditions with a catalyst comprising a Group VIII metal hydrogenatingcomponent supported on a metal-cation-deficient Y zeolite cracking basecontaining less than about 3 weight-percent Na O, and which has beenpreviously calcined while in its metal-cationdeficient and/or precursorammonium form, in the presence of sufficient water vapor to reduce itsunit cell size at least about 0.2 percent, recovering from saidcontacting a desired low-boiling product fraction, and recyclingunconverted oil to said contacting.

2. A process as. defined in claim 1 wherein substantially all of saidunconverted oil is recycled.

3. A. process for hydrocracking a mineral oil feedstock containingdissolved benzcoronenes which comprises contacting said feedstock plusadded hydrogen and under hydrocracking conditions with a catalystcomprising a Group VIII metal hydrogenating component supported on ametal-cation-deficient Y zeolite cracking base containing less thanabout 3 weightpercent Na O, and which has been previously calcined whilein its metal-cation-deficient and/or precursor ammonium form, in thepresence of sufficient water vapor to reduce its unit cell size at leastabout 0.2 percent, recovering from said contacting a desired low-boilingproduct fraction, and recycling unconverted oil to said contacting.

4. A process as defined in claim 3 wherein said calcining is carried outat temperatures of about 1,1 10 1,650F. in the presence of about 5-15psi of water vapor.

5. A process as defined in claim 3 wherein the severity of saidcalcining is controlled so as to reduce the unit cell size and said Yzeolite cracking base by at least about 0.4 percent.

6. A process as defined in claim 3 wherein said Group VIII metal ispalladium and/or platinum.

7. A process as defined in claim 3 wherein said feedstock contains atleast about ppm of benzcoronenes, and wherein substantially all of saidunconverted oil is recycled.

8. A process as defined in claim 3 wherein said Y zeolite cracking baseis at least about 80 percent metalcation-deficient and contains lessthan about 1 percent by weight of sodium as Na O.

9. A process as defined in claim 3 wherein said Group VIII metal ispalladium and/or platinum, said feedstock contains at least about 5 ppmbenzcoronenes, said Y zeolite cracking base is at least about 80 percentmetalcation-deficient and contains less than about one percent by weightof sodium as Na O, and said calcining is controlled so as to reduce theunit cell size of said cracking base by at least about 0.4 percent.

10. A process for hydrocracking a mineral oil feedstock containingdissolved benzcoronenes which comprises contacting said feedstock plusadded hydrogen and under hydrocracking conditions with a catalystcomprising a Group VIII metal hydrogenating component supported on ametal-cation-deficient Y zeolite cracking base, recovering from saidcontacting a desired low-boiling product fraction, and recyclingunconverted oil to said contacting, said Y zeolite cracking base havingbeen prepared by:

1. ion-exchanging a sodium Y zeolite with ammonium salt solution toreduce the sodium content thereof to between about 0.6 percent and 5percent by weight as Na O;

2. calcining the resulting ammonium Y zeolite in the presence ofsufficient water vapor to reduce the unit cell size of the zeolite by atleast about 0.2 percent;

3. subjecting the calcined zeolite to a second ionexchange with ammoniumsalt solution to reduce the sodium content thereof to less than about 3weight-percent as Na O; and

4. calcining the twice-exchanged zeolite under substantially dryconditions to effect deammoniation thereof.

11. A process as defined in claim 10 wherein step (4) is carried outafter intimately admixing the zeolite with a finely divided, hydrousoxide selected from the class consisting of alumina, silica, magnesia,beryllia, zirconia, titania, thoria, chromia, clays and combinationsthereof. 7

12. A process as defined in claim 11 wherein said hydrous oxidecomprises alumina.

13. A process as defined in claim 12 wherein step (2) is carried out attemperatures of about 1,100 1,650F. in the presence of about 5-15 psi ofwater vaper.

14. A process as defined in claim 12 wherein the severity of saidcalcining in step (2) is controlled so as to reduce the unit cell sizeof said Y zeolite cracking base by at least about 0.4 percent.

15. A process as defined in claim 12 wherein said Group VIII metal ispalladium and/or platinum.

16. A process as defined in claim 12 wherein said feedstock contains atleast about 5 ppm of benzcoronenes, and wherein substantially all ofsaid unconverted oil is recycled.

17. A process as defined in claim 12 wherein said Y zeolite crackingbase is at least about percent metalcation-deficient and contains lessthan about one percent by weight of sodium as Na O.

18. A process as defined in claim 12, wherein said Group VIII metal ispalladium and/or platinum, said feedstock contains at least about 5 ppmof benzcoronenes, said Y zeolite cracking base is at least about 80percent metal-cation-deficient and contains less than about one percentby weight of sodium as Na O, and said calcining in step (2) iscontrolled so as to reduce the unit cell size of said cracking base byat least about 0.4 percent.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,793,182 Dated Februarv l9 197 Inventofls) John; W. Ward It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 10,- line 62 (claim "1,110" should be --1,1o0--. Column 10 line67 (claim 5) "and" should be --of--.

si ned aha sealed this llthiday. of June 1971;.

(SEAL) Attest:

EDJARD M.FLE'1GHER,JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents USCOMM-DC OOB'IQoPOQ r us. GOVERNMENT rmmmc OFFICE: 19"o-aGl-au.

FORM PO-IOSO (10-69)

2. A process as defined in claim 1 wherein substantially all of said unconverted oil is recycled.
 2. calcining the resulting ammonium Y zeolite in the presence of sufficient water vapor to reduce the unit cell size of the zeolite by at least about 0.2 percent;
 3. subjecting the calcined zeolite to a second ion-exchange with ammonium salt solution to reduce the sodium content thereof to less than about 3 weight-percent as Na2O; and
 3. A process for hydrocracking a mineral oil feedstock containing dissolved benzcoronenes which comprises contacting said feedstock plus added hydrogen and under hydrocracking conditions with a catalyst comprising a Group VIII metal hydrogenating component supported on a metal-cation-deficient Y zeolite cracking base containing less than about 3 weight-percent Na2O, and which has been previously calcined while in its metal-cation-deficient and/or precursor ammonium form, in the presence of sufficient water vapor to reduce its unit cell size at least about 0.2 percent, recovering from said contacting a desired low-boiling product fraction, and recycling unconverted oil to said contacting.
 4. A process as defined in claim 3 wherein said calcining is carried out at temperatures of about 1,110* - 1,650*F. in the presence of about 5-15 psi of water vapor.
 4. calcining the twice-exchanged zeolite under substantially dry conditions to effect deammoniation thereof.
 5. A process as defined in claim 3 wherein the severity of said calcining is controlled so as to reduce the unit cell size of said Y zeolite cracking base by at least about 0.4 percent.
 6. A process as defined in claim 3 wherein said Group VIII metal is palladium and/or platinum.
 7. A process as defined in claim 3 wherein said feedstock contains at least about 5 ppm of benzcoronenes, and wherein substantially all of said unconverted oil is recycled.
 8. A process as defined in claim 3 wherein said Y zeolite cracking base is at least about 80 percent metal-cation-deficient and contains less than about 1 percent by weight of sodium as Na2O.
 9. A process as defined in claim 3 wherein said Group VIII metal is palladium and/or platinum, said feedstock contains at least about 5 ppm of benzcoronenes, said Y zeolite cracking base is at least about 80 percent metal-cation-deficient and contains less than about one percent by weight of sodium as Na2O, and said calcining is controlled so as to reduce the unit cell size of said cracking base by at least about 0.4 percent.
 10. A process for hydrocracking a mineral oil feedstock containing dissolved benzcoronenes which comprises contacting said feedstock plus added hydrogen and undeR hydrocracking conditions with a catalyst comprising a Group VIII metal hydrogenating component supported on a metal-cation-deficient Y zeolite cracking base, recovering from said contacting a desired low-boiling product fraction, and recycling unconverted oil to said contacting, said Y zeolite cracking base having been prepared by:
 11. A process as defined in claim 10 wherein step (4) is carried out after intimately admixing the zeolite with a finely divided, hydrous oxide selected from the class consisting of alumina, silica, magnesia, beryllia, zirconia, titania, thoria, chromia, clays and combinations thereof.
 12. A process as defined in claim 11 wherein said hydrous oxide comprises alumina.
 13. A process as defined in claim 12 wherein step (2) is carried out at temperatures of about 1,100* - 1,650*F. in the presence of about 5-15 psi of water vapor.
 14. A process as defined in claim 12 wherein the severity of said calcining in step (2) is controlled so as to reduce the unit cell size of said Y zeolite cracking base by at least about 0.4 percent.
 15. A process as defined in claim 12 wherein said Group VIII metal is palladium and/or platinum.
 16. A process as defined in claim 12 wherein said feedstock contains at least about 5 ppm of benzcoronenes, and wherein substantially all of said unconverted oil is recycled.
 17. A process as defined in claim 12 wherein said Y zeolite cracking base is at least about 80 percent metal-cation-deficient and contains less than about one percent by weight of sodium as Na2O.
 18. A process as defined in claim 12 wherein said Group VIII metal is palladium and/or platinum, said feedstock contains at least about 5 ppm of benzcoronenes, said Y zeolite cracking base is at least about 80 percent metal-cation-deficient and contains less than about one percent by weight of sodium as Na2O, and said calcining in step (2) is controlled so as to reduce the unit cell size of said cracking base by at least about 0.4 percent. 